This invention relates to a heterojunction photodiode. More particularly, this invention relates to a PbSnTe photodiode detector for 10.6 .mu.m heterodyne applications.
At the present time, carbon dioxide laser radar, illuminator and communication systems often utilize low temperature extrinsic detectors as a 10.6 .mu.m receiver. However, in most instances, extrinsic detectors do not possess the requisite sensitivity and wide IF bandwidth necessary for modern applications. Furthermore, even in those situations where an extrinsic detector achieves a usable sensitivity and speed, problems are encountered because they require cooling temperatures of between 4.degree. and 30.degree. K.
In accordance with this invention, however, it has been found that the aforementioned problems can be overcome by utilizing an intrinsic detector. An intrinsic detector of PbSnTe offers a higher temperature of operation as well as an energy band gap tunable to the 10.6 .mu.m range. The low operating temperature required for extrinsic detectors eliminates them for most military systems. However, the reverse biased Pb.sub.1.sub.-x Sn.sub.x Te photodiode of this invention fulfills the present need for 77.degree. K. 10.6 .mu.m detectors which are sensitive, fast, have uniform response, and are reliable.